Process for producing cyanoalkylsilanes with a hindered phenol catalyst



United States Patent Ofiice 2,908,700 Patented Oct. 13, 1959 PROCESS FORPRODUCING CYANOALKYL- WITH A PHENOL CAT- 7 ST f1:

No Drawing. Application December 23, 1955 Serial No. 555,208'

15 Claims. (Cl. 260-4482) This invention relates to a process forproducing cyanoalkylsilanes. More particularly, the invention relates toa process for producing cyanoalkylsilanes containing at least onehydrolyzable group bonded to the silicon atom thereof.

By reacting an olefinic nitrile of the type represented byacrylonitrile, methacrylonitrile, crotononitrile and the like with asilane containing at least one hydrogen atom and at least onehydrolyzable group bonded to the silicon atom thereof there is produceda reaction product from which an alpha-cyanoalkylsilane can berecovered. The overall reaction which takes place can be graphicallyrepresented by the following equation, which depicts, for the purpose ofillustration, the reaction between acrylonitrile and trichlorosilane.

The present invention is based on our discovery that an olefinic nitrileor alkene nitrile of the type represented by acrylonitrile,methacrylonitrile, crotononitrile and the like can be caused to reactwith a silane containing at least one hydrogen atom and at least onehydrolyzable group bonded to the silicon atom thereof, in the presenceof a catalyst to produce a beta-cyanoalkylsilane formed by the additionof a silyl group to the beta carbon atom of such nitrile, that is theolefinic carbon atom further removed from the cyano group of thenitrile, and by the addition of a hydrogen atom to the alpha carbon atomof such nitrile, that is the vicinal olefinic carbon atom. Based on ourdiscovery we have further found that any olefinic nitrile can be causedto react with a silane, containing at least one hydrogen atom and atleast one hydrolyzable group bonded to the silicon atom thereof, in thepresence of a catalyst to produce a cyanoalkylsilane by the addition ofa silyl group to the olefinic carbon atom further removed from the cyanogroup of the nitrile napalm 2 Our process can be carried out by forminga mixture of an olefinic nitrile, a silane containing at least onehydrogen atom and at least one hydrolyzable group bonded to the siliconatom thereof and a small or catalytic tert-butyl-4-methylphenol,

amount of a hindered phenol as catalyst for the reaction and heating themixture to a temperature sufliciently elevated to cause the startingmaterials to react. There results. or is produced a-cyanoalkylsilane bythe addition of a silyl group to the olefinic carbon atom of the nitrilefurther removed from the cyano group and by the addition of a hydrogenatom to the olefinic carbon of the nitrile closer to the cyano group.

The silane starting materials, containing at least one hydrogen atom andat least one hydrolyzable group bonded to the silicon atom thereof,which we can employ in the process can be graphically represented by thefollowing general formula:-

RI/IUO (a-) wherein R represents a hydrogen atom or a hydrocarbyl group,preferably a saturated aliphatic hydrocarbyl group as for example, analkyl group, such as methyl, ethyl, propyl, butyl, pentyl and the like;a cycloalkyl group such as cyclopentyl, cyclohexyl, methylcyclopentyl,ethylcyclohexyl, and the like; or an aryl group such as naphthyl, tolyl,methylnaphthyl and the like, X is a hydrolyzable group such as a halogenatom, preferably a chlorine atom; or a hydrocarbyloxy group, preferablyan alkoxy or an aryloxy group such as methoxy, ethoxy, propoxy, phenoxyand the like, and n is a whole number having a value of from 0 to 2.Illustrative of the silane starting materials are trichlorosilane,triethoxysilane, dichlorosilane, di-

' ethoxysilane, monochlorosilane, monoethoxysilane, methis directlybonded through one of the carbon atoms thereof to the carbon atom of thecyano group. Such olefinic nitriles are commonly known as the vinyl-typecyanides and can be represented graphically by the general formula:

where R can be a hydrogen atom or an alkyl group as for example methyl,ethyl, propyl, butyl and the like and A is either a hydrogen atom or amethyl group. Illustrative of such vinyl-type cyanides areacrylonitrile, methacrylonitrile, crotononitrile, and the like.

The hindered phenol compounds which we employ as catalyst in our processdirect the addition of the silyl group of our starting silane to theolefinic carbon atom of our starting nitrile further removed from thecyano group thereof and the addition of the hydrogen atom of thestarting silane to the vicinal olefinic carbon atom. They are thosetri-substituted phenols which contain two large alkyl groups substitutedin the ortho position with respect to the hydroxy group and whichcontain an alkyl group, a cyclohexyl group, an arylpgroup or anotherhindered phenol group substitutedin the para position with respect tothe hydroxy group. Illustrative of such hindered phenols are:2,4,6-tri-tert-butylphenol, 2,6 di- 2,4-di-tert-butyl-6-phenylphenol,2,4-di-tert-butyl 6 cyclohexylphenol, 2,4,6-tri-tertamylphenol,2,4-di-tert-amyl-6-tert-butyl-phenol,2,4-ditert-amyl-6-cyclohexylphenol, 2,6-di-tert-amyl-4-methylphenol,2,6-di-tert-amyl-4-tert-butylphenol, 2-tert-butyl-4-methy1-6-tert-amylphenol, 2,2-methylene-bis(4-methyl-6-tert-butylphenol) and the like.

We have found that the amount of the catalyst employed in our process isnot narrowly critical. Thus, amounts of the hindered phenols of from aslittle as about 0.2 part to as much as about 10 parts by weight per 100parts of the total weight of the starting materials can be favorablyemployed. We preferably employ the catalyst in an amount of from about0.3 part to about 3 parts by weight per 100 parts of the total weight ofthe nitrile and silane starting materials. Amounts of the hinderedphenols in smaller or greater quantities than the favorable range canalso be employed. However, no commensurate advantage is obtainedthereby.

The olefinic nitrile and silane starting materials can be employed inour process in amounts which can vary from about one-half to two molesof the nitrile per mole of the silane. Preferably, the reactants areemployed in equimolar amounts. Amounts of either of the startingmaterials in excess of the ratios set forth above can also be employed;however, no commensurate advantage is obtained thereby.

To facilitate observation and at the same time to favor closer controlof the reaction conditions, most of our experimental work was carriedout in pressure vessels or bombs, with agitation being provided ifdesired by continuous shaking. Similar results can be obtained withflowing reactants in apparatus of known design permitting themaintenance of a closed system. In the reactions with which ourinvention is concerned, it is desirable to maintain sufficiently highconcentrations of the reactants (as measured for example in moles perliter of reaction space) to promote effective contact between themolecules to be reacted. When one of the reactants is a gas, or a liquidreadily volatile at the reaction temperature, and the reaction mixtureispermitted to expand freely on heating, the concentration of thatreactant will fall to a low value thus considerably slowing the reactionrate. If, however, the reactants are charged to a closed vessel which issealed before heating, the initial concentration of any reactant fallsoff through its consumption by the reaction. If a reactant is a gas, itmay be desirable to charge the reaction vessel to a considerablepressure to secure an adequate concentration and reaction rate, and alsoto supply enough of the reactant to produce an acceptable quantity ofthe product.

The temperatures which can be employed in carrying out our process arenot narrowly critical and can vary over a wide range. For example,temperatures as low as 40 C. and as high as 350 C. can be advantageouslyemployed. When conducting the process of the invention in a closedvessel a temperature in the range from about 125 C. to about 250 C. ispreferred. Under such conditions, a reaction period of from about two toabout five hours is suitable. Temperatures of from about 175 C. to about300 C. are preferred when conducting the process in apparatus whichprovides for the flow of the reactants and products while maintainingthe conditions of a closed system. In such systems, where the pressuremay range from atmospheric up to 4000 pounds per square inch and higher,the time required for the reaction to take place can be as short as0.005 minute.

In carrying out the process of our invention the product initiallyobtained comprises a mixture of compounds including the maincyanoalkylsilane reaction product as well as some unreacted nitrile andunreacted silane starting compounds. The desired addition product,formed by the addition of a silyl group to the olefinic carbon atom ofthe nitrile further removed from the cyano group and by the addition ofa hydrogen atom to the olefinic carbon atom closer to the cyano group,which contains at least one hydrolyzable group bonded to the siliconatom thereof, as for example beta-cyanoethyltrichlorosilane, can berecovered from the initially obtained reaction product by a distillationprocedure which is preferably conducted under reduced pressure.

The mechanism of our overall reaction whereby products are produced bythe addition of a silyl group to the olefinic carbon atom of thestarting nitrile further removed from the cyano group and by theaddition of a hydrogen atom to the olefinic carbon atom of the startingnitrile closer to the cyano group with the apparent suppression of otheraddition or reaction products is not known with certainty or fullyunderstood. It is known that upon heating our reactants in the absenceof a hindered phenol as catalyst other reactions take place such as: theformation of both siliconand non-siliconcontaining free radicals andcomplexes, the homopolymerization of the starting nitrile, and even thedisproportionation of the starting silane has been observed. Inaddition, it is known that in the absence of a hindered phenol ascatalyst, our preferred starting materials can react to produce aproduct from which an alpha-cyanoalkylsilane, formed by the addition ofa silyl group to the olefinic carbon closer to the cyano group and bythe addition of a hydrogen atom to the vicinal olefinic carbon, can berecovered with no beta-addition products being formed. One possibleexplanation for the course which our reaction follows when a silane andan olefinic nitrile react in the instance where the nitrile is avinyltype cyanide is that the addition of the silyl group to theolefinic carbon atom more removed from the cyano group of the nitrileoccurs through an ionic mechanism while the addition of such silyl groupto the olefinic carbon atom closer to the cyano group of the nitrileoccurs through a free radical mechanism. If such is the case, then theactivation energy required for the reaction, between our startingnitriles and silanes, to proceed by a free radical mechanism isconsiderably less than that required to cause the reaction to proceed byan ionic mechanism and consequently the reaction between an olefinicnitrile and a silane, as for example acrylonitrile and trichlorosilanewill produce the alpha-addition product namely,alpha-cyanoethyltrichlorosilane. On the other hand, our hindered phenolcatalysts apparently have the effect of markedly decreasing theactivation energy required for the reaction to proceed by an ionicmechanism and therefore when employed in such reactions, as for examplein the above acrylonitrile-trichlorosilane reaction, result in theproduction of beta-cyanoethyltrichlorosilane.

When the olefinic nitrile is of the type represented by allyl cyanide,that is where the unsaturated grouping is removed by one or more carbonatoms from the cyano group, our catalyst also functions in promoting thereaction thereof with our silane starting materials to produce additionproducts by the addition of a silyl group to the olefinic carbon atommore removed from the cyano group, and by the addition of a hydrogenatom to the olefinic carbon closer to the cyano group. By way ofillustration, gamrna-cyanopropyltrichlorosilane is prepared by reactingallyl cyanide with trichlorosilane in the presence of a hindered phenolcatalyst in accordance with the subject process.

Bis(cyanoalkyl)silanes are produced in the practice of the process ofour invention when our starting nitriles are reacted with silanescontaining at least two hydrogen atoms bonded to the silicon atomthereof. In such instances the nitrile starting material is preferablyemployed in an amount of at least twice the number of moles of thestarting silane. The products of the reaction include, in addition tothe desired bis compound, the cyanoalkylhydrogensilane. By way ofillustration, when two moles of acrylonitrile are reacted with one moleof dichlorosilane in the presence of a hindered phenol there isCyanoalkylsilanes, especially the cyanoalkylsilanes in which the silylgroup is bonded to the carbon atom of the nitrile further removed fromthe cyano group thereof, have found particular use as starting materialsin the preparation of omega-aminoalkylsilane sizes for fibrous glassmaterials.

The following examples are illustrative of the present invention.

Example 1 To a 50 cc. steel pressure vessel were added 0.15 moles (7.9g.) of acrylonitrile, 0.15 mole (20.3 g.) of trichlorosilane and 0.56 g.(2 percent by Weight) of di-tert-butyl para cresol. The vessel wassealed and heated to a temperature of 200 C. for a period of two hours.After heating, the vessel was cooled to room temperature and the productremoved therefrom and placed in a flask connected to a distillationcolumn. The contents of the flask were heated to its boiling temperatureunder reduced pressure and there was obtained 5.93 g. of essentiallybeta-cyanoethyltrichlorosilane boiling at a temperature of 75 to 80 C.under areduced pressure of 3 mm. Hg. The 5.93 g. ofbeta-cyanoethyltrichlorosilane represented a yield of 21 percent basedon the total number of moles of the starting materials.

Example 2 To a steel pressure vessel were added equal molar amounts ofacrylonitrile and trichlorosilane together with about 2 percent byweight of the acrylonitrile and trichlorosilane of2,2-methylene-bis(4methyl-6-tert-butylphenyl). The vessel was sealed andheated to a temperature of about 250 C. for a period of two hours. Afterheating, the vessel was cooled to room temperature and the productremoved therefrom and placed in a flask connected to a distillationcolumn. The contents of the flask were heated to its boiling temperatureunder reduced pressure. A yield of 13.4 mole percent ofbeta-cyanoethyltrichlorosilane, based on the total number of moles ofthe starting material, was obtained.

What is claimed is:

1. A process for reacting a silane, represented by the formula:

B ll/(n) where R" represents a member of the group consisting ofhydrogen and a hydrocarbyl group, X represents a hydrolyzable group fromthe class consisting of halogen and hydrocarbyloxy groups and nrepresents a Whole number having a value of from 0 to 2, with an alkenenitrile having from 3 to carbon atoms to produce a cyanoalkylsilane bythe addition of a silyl group to the olefinic carbon atom of saidnitrile further removed from the cyano group thereof and by the additionof a hydrogen atom to the olefinic carbon atom of said nitrile closer tothe cyano group thereof which comprises forming a mixture of saidsilane, said nitrile, and a hindered phenol catalyst, heating saidmixture to a temperature of at least 40 C. to cause said silane andnitrile to react to produce a cyanoalkylsilane by the addition of asilyl group to the olefinic carbon atom further removed from the cyanogroup of the starting nitrile and by the addition of a hydrogen atom tothe olefinic carbon atom closer to the cyano group of the startingnitrile.

2. A process for reacting a silane, represented by the formula:

where R represents a member of the group consisting of hydrogen and ahydrocarbyl group, X represents a hydrolyzable group from the classconsisting of halogen and hydrocarbyloxy groups and n represents a wholenumber having a value of from 0 to 2, with an alkene nitrile having from3 to 10 carbon atoms containing the unsaturated grouping to produce acyanoalkylsilane by the addition of a silyl group to the carbon atom ofsaid unsaturated grouping further removed from the cyano group of saidnitrile and by the addition of a hydrogen atom to the carbon atom ofsaid unsaturated grouping closer to the cyano group of said nitrilewhich comprises forming a mixture of said silane, said nitrile, and ahindered phenol catalyst, heating said mixture to a temperature of fromabout 40 C. to about 350 C. to cause said silane and nitrile to react toproduce a cyanoalkylsilane by the addition of a silyl group to thecarbon atom of the unsaturated grouping further removed from the cyanogroup of the starting nitrile and by the addition of a hydrogen atom tothe carbon atom of the unsaturated grouping closer to the cyano group ofthe starting nitrile and recovering the cyanoalkylsilane.

3. A process for reacting a silane, represented by the formula:

where R represents a member of the group consisting of hydrogen and ahydrocarbyl group, X represents a hydrolyzable group taken from theclass consisting of halogen and hydrocarbyloxy groups and n represents awhole number having a value of from 0 to 2, with a nitrile having from 3to 10 carbon atoms and the formula:

where R is a member of the group consisting of hydrogen and an alkylgroup and A is a member of the group consisting of a hydrogen atom and amethyl group to produce a cyanoalkylsilane by the addition of a silylgroup to the olefinic carbon atom of the nitrile further removed fromthe cyano group thereof and by the addition of a hydrogen atom to theolefinic carbon atom of the nitrile closer to the cyano group thereofwhich comprises forming a mixture of said silane, said nitrile, and ahindered phenol catalyst, heating said mixture to a temperature of fromabout 40 C. to about 350 C. to cause said silane and nitrile to react toproduce a cyanoalkylsilane by the addition of a silyl group to theolefinic carbon atom further removed from the cyano group of thestarting nitrile and by the addition of a hydrogen atom to the olefiniccarbon atom closer to the cyano group of the starting nitrile andrecovering the cyanoalkylsilane.

4. A process for producing a beta-cyanoethylsilane which comprisesforming a mixture comprising a silane of the formula:

where R represents a member of the group consisting of hydrogen and ahydrocarbyl group, X represents a hydrolyzable group taken from theclass consisting of halogen and hydrocarbyloxy groups and n represents aWhole number having a value of from 0 to 2, acrylonitrile and a hinderedphenol catalyst, heating said mixture to a temperature sufiicientlyelevated to cause said silane and acrylonitrile to react to produce abeta-cyanoethylsilane.

5. A process for producing a beta-cyanoethylsilane which comprisesforming a mixture comprising a silane of the formula:

Bil/(n) (3-n) where R' represents a member of the group consisting ofhydrogen and a hydrocarbyl group, X represents a hydrolyzable grouptaken from the class consisting of halogen and hydrocarbyloxy groups andn represents a whole number having a value of from to 2, acrylonitrileand a hindered phenol catalyst, heating said mixture to a temperature offrom about 125 C. to about 300 C. to cause said silane and acrylonitrileto react to produce a beta-cyanoethylsilane and recovering saidbeta-cyanoethylsilane.

6. A process for producing a garrnna-cyanopropylsilane which comprisesforming a mixture comprising a silane of the formula:

where R represents a member of the group consisting of hydrogen and ahydrocarbyl group, X represents a hydrolyzable group taken from theclass consisting of halogen and hydrocarbyloxy groups and n represents awhole number having a value of from 0 to 2, allyl cyanide and a hinderedphenol catalyst, heating said mixture to a temperature of from about 125C. to about 300 C. to cause said silane and allyl cyanide to react toproduce a gamma-cyanopropylsilane.

7. A process for producing beta-cyanoethyltrichlorosilane whichcomprises forming a mixture of acrylonitrile, trichlorosilane and ahindered phenol, heating said mixture to a temperature of from about 125C. to about 300 C. to cause said acrylonitrile and trichlorosilane toreact to produce beta-cyanoethyltrichlorosilane.

8. A process for producing beta-cyanoethyltiiethoxysilane whichcomprises forming a mixture comprising acrylonitrile, triethoxysilaneand a hindered phenol, heating said mixture to a temperature of fromabout 125 C. to about 300 C. to cause said acrylonitrile andtriethoxysilane to react to produce beta-cyanoethyltriethoxysilane.

9. A process for producing beta-cyanoethyltrichlorosilane whichcomprises forming a mixture comprising acrylonitrile, trichlorosilaneand 2,6-di-tert-butyl-4-methylphenol, heating said mixture to atemperature of from about 125 C. to about 300 C. to cause saidacrylonitrile and trichlorosilane to react to producebeta-cyanoethyltrichlorosilane.

10. A process for producing beta-cyanoethyltriethoxysilane whichcomprises forming a mixture comprising acrylonitrile, triethoxysilaneand 2,2-methylene-bis(4- methyl-6-tert-buty1phenol), heating saidmixture to a temperature of from about 125 C. to about 300 C. to causesaid acrylonitrile and triethoxysilane to react to producebeta-cyanoethyltriethoxysilane.

11. A process for producing gamma-cyanopropyltrichlorosilane whichcomprises forming a mixture of allyl cyanide, trichlorosilane anddi-tert-butyl para cresol,

heating said mixture to a temperature of from about C. to about 300 C.to cause said allyl cyanide and trichlorosilane to react to producegamma-cyanopropyltrichlorosilane. I

12. A process for producing a beta-cyanoethylalkyldichlorosilane whichcomprises forming a mixtureof acrylonitrile, alkyldichlorosilane and ahindered phenol, heating said mixture to a temperature of from about 125C. to about 300 C. to cause said acrylonitrile and alkyldichlorosilaneto react to produce a beta-cyanoethylakyldichlorosilane.

13. A process for producing a beta-cyanoethylaryldichlorosilane whichcomprises forming a mixture of acrylonitrile, aryldichlorosilane and ahindred phenol, heating said mixture to a temperature of from about 125C. to about 300 C. to cause said silane and acrylonitrile to react toproduce a beta-cyanoethylaryldichlorosilane.

14. A process for producing beta-cyanoethyltrichlorosilane whichcomprises forming a mixture comprising acrylonitrile, trichlorosilaneand 2,2-methylene-bis(4- methyl-6-tert-butylphenol), heating saidmixture to a temperature of from about 125 C. to about 300 C. to causesaid acrylonitrile and trichlorosilane to react to producebeta-cyanoethyltrichlorosilane.

15. A process for reacting a silane, represented by the formula:

where R' represents a member of the group consisting of hydrogen and ahydrocarbyl group, X represents a hydrolyzable group from the classconsisting of halogen and hydrocarbyloxy groups and n represents a wholenumber having a value of from 0 to 2, with an alkene nitrile having from3 to 10 carbon atoms to produce a cyanoalkylsilane by the addition of asilyl group to the olefinic carbon atom of said nitrile further removedfrom the cyano group thereof and by the addition of a hydrogen atom tothe olefinic carbon atom of said nitrile closer to the cyano groupthereof which comprises forming a mixture of said silane, said nitrile,and a hindered phenol catalyst within a closed system, heating saidmixture to a temperature sufficiently elevated to cause said silane andnitrile to react to produce a cyanoalkylsilane by the addition of asilyl group to the olefinic carbon atom further removed from the cyanogroup of the starting nitrile and by the addition of a hydrogen atom tothe olefinic carbon atom closer to the cyano group of the startingnitrile.

References Cited in the file of this patent UNITED STATES PATENTS2,481,080 Castner et a1. Sept. 6, 1949 2,716,638 Cohen et a1 Aug. 30,1955 2,721,873 MacKenzie et a1. Oct. 25, 1955 2,728,785 Albisetti et a1.Dec. 27, 1955 FOREIGN PATENTS 961,878 France Nov. 8, 1949

1. A PROCESS FOR REACTING A SILANE, REPRESENTED BY THE FORMULA